Method of uniformly bluing coils of embossed sheet steel



Feb. 25, 1964 L. HOLLIS ETAL METHOD 0F UNIFORMLY BLUING COILS OF' EMBOSSED SHEET STEEL Filed May 14, 1962 INVENTORS y LOU/S HOU/S By TED J. /VLDE United States Patent C) 3,i22,459 h/iEHD GF UNIFGRMLY BLUn TG COS @El EMBGSSED SHEET @EBEL Louis Hollis, l-Varren, and Ted J. Noider, Niles, Ghia,

ansignors to Republic Steel Corporation, @escient-l,

Ghia, a corporation of New .iersey Filed May 14, 1962, Ser. No. 194,575 7 Claims. (Cl. 14S-12d The present invention` relates to a method for uniformly blumg coils of sheet steel which have been embossed with a raised pattern. As such, the present invention is a continuation-impart of our prior and copending application Serial No. 20,618, filed April 7, 1960, now US. Patent 3,073,690, although in many respects it may also be considered as a division thereof but with minor variations therefrom.

In our prior application a method and apparatus were described and claimed for preparing suitable rolls for rolling sheet metal, wherein each roll had a plurality of diamond-shaped recesses therein, so that the sheet metal rolled thereby would have a corresponding pattern of diamond-shaped raised portions. From the point of View of the present invention, the shape of the raised portions is not material, although the diamond shape of our parent application is fully applicable and is presently considered desirable Vfor use in the present invention. The raised portions of the embossing as taught in the present application may be on one or both surfaces of the sheet steel used in the present method and may be formed in any way ltnown to the art including the manner and by the use of equipment as taught in the parent application aforesaid.

In accordance with the prior practice of bluing steel in sheet form, the sheet steel rolled in substantially tight rolls was first annealed, then, with its temperature controlled to a predetermined range, was subjected to the action of steam, the latter action taking place after sui"- ably purging the zone surrounding the sheet being treated by a non-oxidizing gas so that the steam treatment is conducted out of Contact with oxygen or other oxidizing gases. Following the steam treatment, the steam was purged and the steel cooled under non-oxidizing conditions.

lt has been found that when sheet steel was rolled in relatively tight coils, the results of the Well-known bluing process generally described hereinabove were somewhat indenite and the bluing was not uniform. It has now been determined that the reason for this non-uniformity of this bluing process Was that no provision was made in the customary tight coils of steel for providing reasonable access to all portions of the steel sheets being treated for the bluing gases, i.e. the steam during the steam treatment and/ or the deoxidizing and/ or reducing gases used betere and after the steam. It has been found, in accordance with the present invention, that when sheet steel, embossed on at least one side with raised embossed portions, is formed into coils as tight as those conventionally formed in the commercial manufacture of steel sheets, and where the embossing portions are raised above the sheet surfaces as little as about 0.003 to about 0.02 inch, adequate provision is thereby made for access of the gases to all portions of the sheet surface, so that the resulting bluing operation, which is done otherwise Cil 3,122,459 Patented Feb. 25, 1964 ICC in a substantially conventional manner in 'accordance with the prior art practices for bluing steel, results in the making of uniformly blued sheets, thus overcoming the diiiiculties of non-uniform bluing experienced by the prior art. It is preferred in this process that the steel used be embossed on both sides, although this is not necessary.

Another step in the process which has been found desirable in forming blued steel sheets according tothe present invention, particularly Where the ultimate customer desires a substantially smooth and strong sheet, is to form the sheet initially with suitably shaped raised portions, for example, the diamond-shaped portions referred to aforesaid; then to blue the embossed sheets as hereinafter set out; then to reroll the blued sheets after they have fully cooled, using for this rerolling smooth rolls which will smooth down the embossed pattern to form a substantially uniform surface sheet from the point of view of the feel of the sheet and from the point of view of the thickness or relative thickness of various parts thereof. On the other hand, the appearance of the original embossed pattern, which is sometimes considered attractive from the point of View of many steel users, remains optically apparent even after this smooth rolling as described, so that the final sheet is 1olued, is smooth, but has a desired pattern, corresponding to the pattern of the original embossing of the sheet and which is clearly visible to users of the sheet and forms with the blue surface appearance, a desired finish. It has also been found that this final roll or temper rolling, as it is sometimes called, serves by reason of the cold working of the sheet, to give the sheet certain superior physical characteristics such as increased hardness which is not a characteristic of the sheet prior to the cold rolling aforesaid.

Other features and advantages of the present invention as Well as equivalents of various portions of the process will be pointed out as the following description proceeds, this description being coordinated with the accompanying drawings, in which:

FIG. 1 is a View of a inutile-type construction used during the process of annealing and bluing steel sheets in coil form, the view `eing taken in vertical section as to the mame substantially on the line 1*1 of FIG. 2, but showing the steel coils in elevation;

FIG. 2 is a view of the muie of FIG. 1 taken on a reduced scale and substantially in plan;

FIG. 3 is a fragmentary detailed View of a portion of a steel sheet taken as a face view thereof and is representative both of the appearance of the sheet with raised portions and also of a sheet after it has been rolled smooth subsequent to the bluing operation, but with the previously raised, diamond-shaped portions ilattened into the plane of the sheet, but still optically apparent; and

FG. 4 is a fragmentary view taken substantially on the line 4 4 of FIG. 1, but on an enlarged scale showing several turns of a sheet of steel in a tight coil, wherein both surfaces of the sheet steel are provided with embossed raised portions.

In the accompanying drawings, an embossed sheet of steel such as the product of the process of our parent application aforesaid is illustrated in FIGS. 3 and 4. As shown in these drawings, and particularly in FiG. 4, the sheet is embossed on both surfaces, although this is not essential from the point of View of the present invention.

Embossing on only one surface, if reasonably deep as hereinafter set forth, is adequate to secure the desired results of the present process. The depth of embossing is preferably from about 0.003 inch to about 0.02 inch and preferably at least about 0.015 inch when only one surface is embossed. The lower ranges of thickness of embossing are suitable and adequate when both surfaces are embossed. It will be understood that from the point of view of the present invention, the embossing may be effected in any vsuitable way, preferably by rolling the sheets with suitably shaped or formed embossing rolls. In FIG. 3 of the present drawings the embossed pattern sheet is shown at 40.

It is usual in rolling mill operation in the handling of sheet steel to roll up the sheets into relatively tight coils after the sheets have been passed through the rolls and/ or are otherwise suitably embossed. These tight coils may then be handled by conventional apparatus which is customarily used in steel mill operation. Because of the cold rolling to which these sheets, or many of them at least, have been subjected, the rirst operation which needs to be accomplished in many, if not all, instances is to anneal the sheets, which is done with the sheet in the form of tight coils and with the coiled sheet conveniently held in a sort of muifle or closed chamber, although this prevention of contact with the atmosphere during the annealing per se is not essential.

To this end, relatively large and heavy bottom members 41 of metal, such as iron or steel, are used and have piled thereon a plurality of coils of steel sheets, for example, the coils 42, 43, 44, 45 and 46 (FIGS. l and 2) in any desired manner, so as preferably substantially to fill the interior of the closed compartment or muille formed by the member 41 and a cover member 47. Each of the cover members 47 is of substantially one piece (possibly built as a welded construction) and is of metal. These cover members are sufficiently heavy so as to be retained in position by their own weight, surrounding the coils of steel to be annealed and/or otherwise treated. It is also preferred that the space between the lower edge portion 4S of each cover member 47 and an upstanding flange 49 of the member 41 shall be lled with a sealing material S as sand or the like. It will be appreciated that this seal is not air-tight and in fact it is not intended to be. However, when a gaseous material is supplied to the interior of the cover 47, for example through an inlet pipe 51, FIG. l, the establishment of a slight but positive superatmospheric pressure within the cover member 47 and about the coils 42-46 inclusive will result in the prevention of ingress of atmospheric air through the sealing material 50.

As stated above, the annealing per se may be done either in the presence of air or after purging the inside of the muihe with a non-oxidizing gas. ln any event, after the annealing is completed and prior to the next succeeding operation as hereinafter set out, it is necessary to purge the inside of the mule formed by the cover member 47 and the bottom member 41 and about the steel coils or sheets by supplying a non-oxidizing gas through the pipe 51 at a pressure which is suiciently above atmospheric so that it will serve to purge all the air therefrom, forcing it gradually out through gas-pervious sealing material 50. At the same time, the pressure within the muie formed by the cover member 47 is so close to atmospheric that there will never be enough internal pressure to blow the sealing material 50 out of place. The sand seal 50 is, therefore, preferably somewhat gas-pervious to enable the operation to be carried on as described.

` With the coils of steel arranged in any desired manner within the mufhe and either before or after the interior of Vthe mutle is substantially purged of oxygen or oxygencontaining gases by the admission of a non-oxidizing gas of any desired nature or composition, but one which will not chemically attack the steel, the entire apparatus or muflle, including the base member 4l and the cover member 47 with the steel therein, is moved into an annealing furnace, so that the temperature of the steel may be brought up to and held at an annealing temperature for a period of time suicient to effect the desired annealing of the sheets. This in practice is done for a period of about 10 to 12 hours and at about 1200 F. It will be understood of course that this t'une is not at all critical and further, that the temperature must be sufficiently high to effect the desired annealing, but not high enough to permit substantial distortion of the sheets under any stresses to which they may be subjected during the time they are at the higher temperature.

Following the annealing as aforesaid, the sheets are cooled in the mule as described; and in the event that purging has not previously been done, it should be done at this time. Thus during and to some extent to effect this cooling, a cool (room temperature) non-oxidizing gas is supplied to the interior of the muliie which affects both the cooling of the steel and the purging of the oxidizing gases from inside the muiie. This operation normally takes place during about 6 hours. The duration of the cooling period is not critical, as it is important merely that the sheets be cooled to a temperature in the range of 550-850 F. and that the oxidizing gases be purged from the interior or" the muftle, both prior to the initiation of the bluing operation which is a principal feature of the present invention.

This bluing is effected starting at a temperature in the range of about SSW-850 F. by subjecting the steel to intimate contact with steam which may be supplied to the interior of the mule through the pipe 51 or a pipe of similar character, so as substantially to purge from the interior of this muifle all of the deoxidizing gas aforesaid by forcing it out through the gas-pervious sealing material 50 incident to the supplying into the interior of the muie of steam at a relatively low pressure. The temperature of the steam is apparently not particularly critical as the treating temperature per se is largely governed by the temperature of the steel and its surrounding muflle. The pressure of the steam again should be somewhat superatmospheric, but not sutliciently so to dislodge any substantial portion of the sand or other sealing material S0'.

When the bluing operation is to be started, the supply of the deoxidizing gas aforesaid to the interior of the muifle is cut off and the supply of steam, coupled with the further permissive cooling of the steel sheets, is carried on for a period of about a day (twenty-four hours). Again, the exact time is not at all critical. It is, however, necessary that the deoxidizing gas and more particularly the steam shall have intimate contact with all portions of the steel sheets in order that the bluing resulting therefrom shall be uniform. When sheets in the form of tight coils were used in this process inthe prior art without ade- Y that the bluing resulting from the practice of the processY was non-uniform and in general, correspondingly unsatisfactory. By having even one side of each of the sheets provided with embossed portions as shown for the several coils provided with embossed portions 52, and otherwise close together as shown for the several turns S3, 54 and 55 of the coil shown in FIG. 4, it is found that there is a suicient access for the gases to all portions of the sheet surfaces, so that the results of the bluing operation are substantially uniform, at least to the naked eye. The height of the raised portions required to effect this uniform bluing is (as a minimum) in the range of 0.003 inch to 0.02 inch as aforesaid. Under these conditions and when only one side of such a sheet is so embossed, substantially uniform bluing is attained. It is preferred, however, that both sides of the sheet be so embossed, so that there will be no question, but that access will be had by the bluing gases, i.e. the deoxidizing gas followed by the steam, and so that assured uniform bluing will result.

Following the steam treatment as aforesaid, the supply of steam to the muie is cut olf and any steam remaining therein is purged from the interior of the muile by the use of a substantially dry and preferably cool (room temperature) deoxidizing gas of any desired composition, except that it must be deoxidizing in character so as to be substantially chemically neutral as far as the steel sheets and their blued surfaces are concerned. This dry dcoxidizing gas is continuously supplied to the interior of the mufe, as through the pipe 51, and at a pressure slightly above atmospheric as aforesaid so as to purge the steam therefrom.

During all this period the steel sheets are continuously but permissibly cooled. This treatment with the dry deoxidizing gas is ordinarily conducted for a period of about eight hours, which results in bringing the temperature of the steel down to the point where it will not be damaged by direct contact with the atmosphere. After this the cover member 47 may be removed and the steel moved or otherwise handled in any desired way as in conventional steel mill practice.

The steel so prepared may be used as such if the customer desires or is willing to accept embossed steel sheets. If, however, the customer desires a steel sheet which is essentially smooth on one or both sides, and particularly does not desire a sheet having embossed, raised portions thereon, it may be desired at this stage of the operation to run the blued sheets through a rolling mill provided with smooth rolls which will flatten the embossed portions out and serve to render the sheet substantially smooth on one or both sides, while still retaining the appearance of the embossed portions from a solely optical point of view. In other words, the sheet thus further smoothrolled will have a pattern thereon which is optically equivalent to the embossed pattern in that it is optically apparent, but is not represented by actual raised or embossed portions, as the sheet will be essentially smooth in character. Such sheets have found favor with many users of steel, so that the production of such sheets is one of the objects of the present invention.

The subsequent rolling operation just described serves not only to smooth one or both surfaces of the sheet, but also acts as a cold rolling operation (to an extent dependent upon an amount of reduction of the thickness of the sheet effected in this rolling operation), so as to give the sheet the physical characteristics of cold-rolled steel (increased hardness, etc.). This subsequent rolling is sometimes known as temper rolling.

While there is herein disclosed but one principal embodiment of the present invention, an attempt has been made as the description proceeded to point out alternatives of various features thereof. It is recognized that other alternatives or equivalents will occur to those skilled in the art from the foregoing particular disclosure. We do not wish to be limited, therefore, except by the scope of the appended claims, which are to be construed validly as broadly as the state of the art permits.

What is claimed is: Y

1. The method of uniformly bluing sheet steel in the form of a relatively tight coil, comprising the steps of forming the sheet steel with an embossed surface pattern on at least one surface thereof, said embossed portions being raised above the steel surfaces from about 0.003 to about 0.02 inch so that when the sheet is coiled tightly, the embossing will permit penetration of treating gases to substantially all parts of the sheet, enclosing said tight embossed coil in a munie, bringing the temperature of the coil in the muie to the range of about 550-850 F.; purging all air and oxidizing gases from inside the mur'i'le by iiushing it with a deoxidizing gas; cutting off the supply of said deoxidizing gas to the inutile and supplying thereto relatively low pressure steam for about a day, whereby all portions of the sheet surfaces are substantially uni- Vformly blued, to the naked eye; purging the steam from inside the mue by flushing with a substantially dry deoxidizing gas; cooling the blued sheet steel at least to a temperature where it will not be damaged by direct contact with the atmosphere; and thereafter removing substantially cooled and uniformly blued sheet steel coil from the mufflc.

2. The method of uniformly bluing sheet steel in accordance with claim l, comprising forming embossed surface patterns on both surfaces of the sheet.

3. The method of uniformly bluing sheet steel in accordance with claim l, further comprising the step of rolling the sheet steel which was blued as aforesaid between smooth rolls to reduce the height of the raised embossed portions to the point where each previously embossed sheet surface is substantially smooth, but with the previously embossed pattern still optically apparent.

4. The method of uniformly bluing sheet steel in accordance with claim 1, in which both surfaces of the sheet steel are embossed as aforesaid with the raised portions of the embossing at a height of about 0.015 inch above the surface of the sheet, and comprising the further step of rolling the sheet steel which was blued as aforesaid between smooth rolls to reduce the height of the raised embossed portions to the point where each previously embossed sheet surface is substantially smooth, but with the embossed pattern still optically apparent.

5. The method of annealing and uniformly bluing sheet steel in the form of a relatively tight coil, comprising the steps of forming the sheet steel with an embossed surface pattern where the embossed portions are raised above the sheet surfaces from about 0.003 to about 0.02 inch on at least one surface thereof, so that when the embossed sheet is coiled tightly, the embossing will permit penetration of treating gases to substantially all parts of the sheet, enclosing said tight embossed coil in a muflle, annealing the sheet by bringing the temperature of the steel coil to and holding it at a temperature of about 1200 F. for about 10 to l2 hours; purging all air and oxidizing gases from inside the inutile by flushing it with a deoxidizing gas While cooling it to a temperature i-n the range of about 550-850 F.; cutting otf the supply of deoxidizing gas to the muille and supplying thereto relatively low pressure steam for about a day, so that all portions of the sheet surfaces are substantially uniformly blued, to the naked eye, while permitting continued slow cooling of the muie and its contents; cutting off the supply of steam to the muifle and purging it therefrom with a substantially dry deoxidizing gas, while continuing the permissive cooling of the sheet steel in the muiile for about 8 hours; and thereafter exposing the so-treated and substantially cooled and uniformly blued steel coil to the atmosphere.

6. The method of annealing and uniformly bluing sheet steel in accordance with claim 5, comprising forming said embossed pattern on both surfaces of the sheet steel, said embossed pattern being a plurality of substantially diamond-shaped raised portions in each instance with said raised portions extending above other portions of the sheet by about 0.015 inch; and rolling the sheet steel which was blued as aforesaid between smooth rolls to reduce the height of the raised embossed portions to the point where each previously embossed sheet surface is substantially smooth, but with the previously embossed pattern still optically apparent.

7. The method of annealing and uniformly bluing sheet steel in the form of a relatively tight coil, comprising the steps of forming the sheet steel with an embossed surface pattern on at least one surface thereof where the embossed portions are raised above the sheet surfaces from about 0.003 to about 0.02 inch, so that when the sheet is coiled tightly, the embossing will permit penetration of treating gases to substantially all parts of the sheet, enclosing said tight embossed coil in a muie, purging all air and oxidizing gases from inside the mufiie by ushing it with a deoxidizing gas, annealing the coiled sheet within the muflle by bringing it to a temperature of about 1200 F. for about 10-12 hours, thereafter cooling the steel in the mue to a temperature in the range of about 550-850 F.; cutting 01T the supply of deoxidizing gas to the mulle and supplying thereto relatively low pressure steam for about a day, so that all portions of the sheet surfaces are substantially uniformly blued, to the naked eye, while permitting continued slow cooling of the munie and its contents; cutting olf the supply of steam to the mule and purging steam therefrom with a sub- 10 2,333,936

8 stantially dry deoxidizing gas, while continuing the pen missive cooling of the blued sheet steel in the mule for about 8 hours; and thereafter exposing the so-treated and substantially cooled and uniformly blued steel to the at- 5 mosphere.

References Cited in the le of this patent UNITED STATES PATENTS Fahrenwald Dec. 16, 1930 Johnson Nov. 9, 1943 

1. THE METHOD OF UNIFORMLY BLUING SHEET STEEL IN THE FORM OF A RELATIVELY TIGHT COIL, COMPRISING THE STEPS OF FORMING THE SHEET STEEL WITH AN EMBOSSED SURFACE PATTERN ON AT LEAST ONE SURFACE THEREOF, SAID EMBOSSED PORTIONS BEING RAISED ABOVE THE STEEL SURFACES ROM ABOUT 0.003 TO ABOUT 0.02 INCH SO THAT WHEN THE SHEET IS COILED TIGHTLY, THE EMBOSSING WILL PERMIT PENETRATION OF TREATING GASES TO SUBSTANTIALLY ALL PARTS OF THE SHEET, ENCLOSING SAID TIGHT EMBOSSED COIL IN A MUFFLE, BRINGING THE TEMPERATURE OF THE COIL IN THE MUFFLE TO THE RANGE OF ABOUT 550*-850*F.; PURGING ALL AIR AND OXIDIZING GASES FROM INSIDE THE MUFFLE BY FLUSHING IT WITH A DEOXIDIZING GAS; CUTTING OFF THE SUPPLY OF SAID DEOXIDIZING GAS TO THE MUFFLE AND SUPPLYING THERETO RELATIVELY LOW PRESSURE STEAM FOR ABOUT A DAY, WHEREBY ALL PORTIONS OF THE SHEET SURFACES ARE SUBSTANTIALLY UNIFORMLY BLUED, TO THE NAKED EYE; PURGING THE STEAM FROM INSIDE THE MUFFLE BY FLUSHING WITH A SUBSTANTIALLY DRY DEOXIDIZING GAS; COOLING THE BLUED SHEET STEEL AT LEAST TO A TEMPERATURE WHERE IT WILL NOT BE DAMAGED BY DIRECT CONTACT WITH THE ATMOSPHERE; AND THEREAFTER REMOVING SUBSTANTIALLY COOLED AND UNIFORMLY BLUED SHEET STEEL COIL FROM THE MUFFLE. 